The present invention relates to a booster for use in a brake mechanism of a vehicle. More particularly, the present invention relates to an electric booster using an electric motor as a boosting source and a method for manufacturing the electric booster.
Conventionally, many brake mechanisms of vehicles have employed a vacuum booster capable of generating output boosted relative to input by utilizing a negative pressure in an engine inlet pipe. However, recently, engine development focusing on fuel-efficient improvement, exhaust-gas cleaning and the like has been advancing, with the consequence that a negative pressure in an inlet pipe tends to be reduced. Therefore, some measures such as increasing a booster size, increasing a negative pressure with use of an ejector, and providing a vacuum pump being driven by an engine, etc need to be taken in order to obtain a desired boosting performance or response as a vacuum booster. As an inevitable result of such measures, installability of a vacuum booster onto a vehicle deteriorates, and cost of a vacuum booster becomes more expensive.
Therefore, in recent years, an electric booster using an electric motor as a boosting source has attracted attention. As such an electric booster, for example, Japanese Patent Application Public Disclosure No. SHO61-143253 discloses an electric booster in which an electric motor is driven in response to a displacement of an input member caused by a movement of a brake pedal, a piston in a master cylinder is thrust through a ball screw mechanism (rotation-linear motion converting mechanism), and a brake hydraulic pressure is generated in the master cylinder.